This practical will introduce the topic of sexual differentiation during development through a series of online resource pages.
Aim: This practical is an introduction to the earliest events in Sexual Differentiation.
Key Concepts: primordial germ cell, sex chromosomes, gonad, internal genitalia, external genitalia, ovary, testis, puberty, hormonal changes, gametogenesis, genital abnormalities (DSD).
Historic Gonad Images
|Two key systems, neural and reproductive, develop over an extended period from the early embryo to puberty and the emerging adult. The genital system is closely linked developmentally to the urinary system, often called the urogenital system. This practical will therefore cover early development of both system.
In understanding embryonic sexual development, think of a cascade of sequence dependent events that transform indifferent gonads, internal and external genitalia into distinct male and female structures.
The process begins with gonad differentiation, which itself is tied developmentally back at the initial event of fertilization and the presence of either a Y or X chromosome in the sperm.
The endpoint of development could be considered the post-puberty active reproductive system. Interestingly, recent research is pointing to a link between neural and reproductive systems in how male and female brains may differentially develop under the influence of sex hormones and perhaps even the sex chromosomes.
- There are 6 pages to work through in today's practical class, listed beside the small BGD icon at the top and bottom of each page.
- Additional information sections are not part of the practical class content.
These are approximate timings and stages only.
- 24 days - intermediate mesoderm, pronephros primordium
- 28 days - mesonephros and mesonephric duct
- 35 days - uteric bud, metanephros, urogenital ridge
- 42 days - cloacal divison, gonadal primordium (indifferent)
- 49 days - paramesonephric duct, gonadal differentiation
- 56 days - paramesonephric duct fusion (female)
- 100 days - primary follicles (ovary)
- postnatal 2 months of age - male primordial germ cells (gonocytes) are replaced by adult dark (Ad) and pale (Ap) spermatogonia forming the spermatogonial stem cell (SSC) population.
||Hill, M.A. (2020). UNSW Embryology (20th ed.) Retrieved December 11, 2023, from https://embryology.med.unsw.edu.au
||Moore, K.L., Persaud, T.V.N. & Torchia, M.G. (2015). The developing human: clinically oriented embryology (10th ed.). Philadelphia: Saunders. (links only function with UNSW connection)
Chapter 12 Urogenital System
||Schoenwolf, G.C., Bleyl, S.B., Brauer, P.R., Francis-West, P.H. & Philippa H. (2015). Larsen's human embryology (5th ed.). New York; Edinburgh: Churchill Livingstone.(links only function with UNSW connection)
Chapter 15 Development of the Urinary System
Chapter 16 Development of the Reproductive System
||Nussey, S and Saffron Whitehead, S. Endocrinology: An Integrated Approach. Oxford: BIOS Scientific Publishers; 2001.
Chapter 6 The gonad
BGDB: Lecture - Gastrointestinal System | Practical - Gastrointestinal System | Lecture - Face and Ear | Practical - Face and Ear | Lecture - Endocrine | Lecture - Sexual Differentiation | Practical - Sexual Differentiation | Tutorial
- Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link
Cite this page: Hill, M.A. (2023, December 11) Embryology BGDB Practical - Sexual Differentiation. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDB_Practical_-_Sexual_Differentiation
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- © Dr Mark Hill 2023, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G